Peroxycarboxylic acid compositions can be effective antimicrobial agents. Methods of using peroxycarboxylic acids to clean, disinfect, and/or sanitize hard surfaces, textiles, meat products, living plant tissues, and medical devices against undesirable microbial growth have been described (U.S. Pat. No. 6,545,047; U.S. Pat. No. 6,183,807; U.S. Pat. No. 6,518,307; U.S. Patent Application Publication No. 20030026846; and U.S. Pat. No. 5,683,724). Peroxycarboxylic acids have also used in a various laundry care applications, such as their use as bleaching agents (U.S. Pat. No. 3,974,082; U.S. Pat. No. 5,296,161; and U.S. Pat. No. 5,364,554).
Peroxycarboxylic acids can be prepared by the chemical reaction of a carboxylic acid alkyl ester and a peroxide reagent, such as hydrogen peroxide (see Organic Peroxides, Daniel Swern, ed., Vol. 1, pp 313-516; Wiley Interscience, New York, 1971). However, under slightly basic to acidic pH (from about 8 to about 4) the reaction often does not proceed rapidly enough to produce a peroxycarboxylic acid concentration that is suitable for many commercial disinfecting and/or bleaching applications.
One way to overcome the disadvantages of chemical peroxycarboxylic acid production is to use an enzyme catalyst having perhydrolysis activity. U.S. patent application Ser. No. 11/638,635 and U.S. Patent Application Publication Nos. 2008/0176783; 2008/0176299; and 2009/0005590 to DiCosimo et al. disclose enzymes structurally classified as members of the CE-7 family of carbohydrate esterases (e.g., cephalosporin C deacetylases [CAHs] and acetyl xylan esterases [AXEs]) that are characterized by significant perhydrolysis activity for converting carboxylic acid esters (in the presence of a suitable source of peroxygen, such as hydrogen peroxide) into peroxycarboxylic acids at concentrations sufficient for use as a disinfectant and/or a bleaching agent. Some members of the CE-7 family of carbohydrate esterases have been demonstrated to have perhydrolytic activity sufficient to produce 4000-5000 ppm peracetic acid from acetyl esters of alcohols, diols, and glycerols in 1 min and up to 9000 ppm between 5 minutes and 30 minutes once the reaction components were mixed (DiCosimo et al., U.S. Patent Application Publication No. 2009/0005590). CE-7 perhydrolases will often produce increasing concentrations of peracids after 30 minutes or more under suitable aqueous reaction conditions that include excess substrate, a pH of about 6.0 to about 8.5, and suitable temperature range. Typically the pH of the reaction is maintained using an effective amount of at least one buffer. The amount of peroxyacetic acid produced using such conditions may exceed that which is desirable or may take too long to eventually reach an efficacious concentration for certain applications.
Enzymatic production of peroxycarboxylic acids (e.g., peracetic acid) is typically conducted using aqueous reaction conditions. As such, hydrolysis reactions (chemical and/or enzymatic) often occur that produce the corresponding carboxylic acid (e.g., acetic acid) from the hydrolysis of the ester substrate and/or hydrolysis of the peroxycarboxylic acid, thereby destroying the desired product. The products of enzymatic perhydrolysis (peroxycarboxylic acid or a mixture of the peroxycarboxylic acid and the corresponding carboxylic acid hydrolysis product) can be corrosive to certain metal surfaces. As such, it may be desirable to limit the total amount of peroxycarboxylic acid produced during the reaction to prevent or minimize the corrosive effect of the resulting solution. For example, applications that require production of no more than 200 ppm to 1000 ppm of peracid in 1 minute often employ reaction conditions that yield a final concentration of peracid well above these limits. In an application for in situ generation of peracid for disinfection of hard surfaces, it is desirable to have the ability to rapidly generate the desired concentration of peracid without significantly exceeding the upper efficacious disinfectant concentration, thereby limiting or preventing the corrosion of certain components of the surface. In an application for in situ generation of peracid for bleaching of laundry or textiles, similar limitations to the concentration of peracid generated above that required for bleaching are also desirable. As such, there is a need to provide a process to rapidly produce a desired “target” concentration of peroxycarboxylic acid, especially in the presence of excess substrate.
Many CE-7 carbohydrate esterases exhibit a decrease or inactivation in perhydrolysis activity when the pH drops below about 6.0 with most of the CE-7 perhydrolases inactivated at or below a pH of 5.0. U.S. patent application Ser. No. 12/539,025 to DiCosimo et al. teaches a process to produce a desired “target” concentration of peroxycarboxylic acid by selecting reaction components and conditions whereby reaction products are formed (i.e., the peroxycarboxylic acid and the corresponding carboxylic acid hydrolysis product) that drop the pH of the reaction mixture to value where the enzyme catalyst has little or no perhydrolysis activity. The reaction components and conditions are selected whereby the pH of the reaction mixture drops below 6.0 within 10 minutes or less, enabling one to control the concentration of peroxycarboxylic acid produced. However, a product mixture having a pH of less than 6.0 may not be desirable for some disinfecting and/or bleaching applications, especially when the surface in contact with the reaction products is susceptible to corrosion and excessive bleaching. Under such circumstances, there remains a need to control the amount of enzymatically produced peroxycarboxylic acid that is not dependent on a substantial drop in the pH of the reaction mixture.
The problem to be solved is to provide a process to enzymatically produce a desired concentration of peroxycarboxylic acid in an aqueous reaction mixture that is not dependent upon a significant drop in pH or a pH of less than 6.0. The selected reaction components and reaction conditions should be capable of rapidly producing the desired peroxycarboxylic acid at a concentration that does not substantially increase once the target concentration is achieved.